>Vagus nerve stimulation (VNS) is an effective adjunctive treatment for medically refractory epilepsy. In this study, we measured VNS-induced changes in hippocampal neurotransmitter levels and determined their potential involvement in the anticonvulsive action of VNS, to elucidate the mechanism of action responsible for the seizure suppressing effect of VNS in an animal model for limbic seizures. We used in vivo intracerebral microdialysis to measure VNS-induced changes in hippocampal extracellular concentrations of noradrenaline, dopamine, serotonin and GABA in freely moving, male Wistar rats. During the same experiment, the effect of VNS on pilocarpine-induced limbic seizures was assessed using video-EEG monitoring. The involvement of VNS-induced increases in hippocampal noradrenaline in the mechanims of action of VNS was evaluated by blocking hippocampal alpha(2)-receptors. VNS produced a significant increase in hippocampal noradrenaline concentration (69 +/- 16% above baseline levels). VNS also increased the latency between pilocarpine infusion and the onset of epileptiform discharges, and reduced the duration and severity of pilocarpine-induced limbic seizures. A strong positive correlation was found between the noradrenergic and anticonvulsive effects of VNS. Blockade of hippocampal alpha(2)-receptors reversed the seizure-suppressing effect of VNS. VNS induces increases in extracellular hippocampal noradrenaline, which are at least partly responsible for its seizure-suppressing effect in a model for limbic seizures, and constitute a potential biomarker for the efficacy of VNS in temporal lobe epilepsy.

@article{1228308,
abstract = {{\textrangle}Vagus nerve stimulation (VNS) is an effective adjunctive treatment for medically refractory epilepsy. In this study, we measured VNS-induced changes in hippocampal neurotransmitter levels and determined their potential involvement in the anticonvulsive action of VNS, to elucidate the mechanism of action responsible for the seizure suppressing effect of VNS in an animal model for limbic seizures. We used in vivo intracerebral microdialysis to measure VNS-induced changes in hippocampal extracellular concentrations of noradrenaline, dopamine, serotonin and GABA in freely moving, male Wistar rats. During the same experiment, the effect of VNS on pilocarpine-induced limbic seizures was assessed using video-EEG monitoring. The involvement of VNS-induced increases in hippocampal noradrenaline in the mechanims of action of VNS was evaluated by blocking hippocampal alpha(2)-receptors. VNS produced a significant increase in hippocampal noradrenaline concentration (69 +/- 16\% above baseline levels). VNS also increased the latency between pilocarpine infusion and the onset of epileptiform discharges, and reduced the duration and severity of pilocarpine-induced limbic seizures. A strong positive correlation was found between the noradrenergic and anticonvulsive effects of VNS. Blockade of hippocampal alpha(2)-receptors reversed the seizure-suppressing effect of VNS. VNS induces increases in extracellular hippocampal noradrenaline, which are at least partly responsible for its seizure-suppressing effect in a model for limbic seizures, and constitute a potential biomarker for the efficacy of VNS in temporal lobe epilepsy.},
author = {Raedt, Robrecht and Clinckers, Ralf and Mollet, Lies and Vonck, Kristl and EL TAHRY, RIEM and Wyckhuys, Tine and De Herdt, Veerle and Carrette, Evelien and Wadman, Wyste and Michotte, Yvette and Smolders, Ilse and Boon, Paul and Meurs, Alfred},
issn = {0022-3042},
journal = {JOURNAL OF NEUROCHEMISTRY},
keyword = {REFRACTORY EPILEPSY,LOCUS-CERULEUS GRAFTS,NORADRENERGIC TRANSMISSION,FREELY MOVING RATS,PILOCARPINE-INDUCED SEIZURES,vagus nerve stimulation,pilocarpine,temporal lobe epilepsy,KINDLING EPILEPSY,AMINO-ACIDS,BRAIN-STEM,NOREPINEPHRINE,COERULEUS,EEG,Hippocampus,noradrenaline},
language = {eng},
number = {3},
pages = {461--469},
title = {Increased hippocampal noradrenaline is a biomarker for efficacy of vagus nerve stimulation in a limbic seizure model},
url = {http://dx.doi.org/10.1111/j.1471-4159.2011.07214.x},
volume = {117},
year = {2011},
}